CONFORMATIONAL CONTROL IN THE SYNTHESIS OF MIXED TETRAETHERS OF CALIX[4]ARENE .2.

A series of mixed tetraethers of calix[4]arene and p-tert-butylcalix[4 ]arene in which two distal substituents are methyl and the other two 1 -alkenyl groups with 3, 4 and 5 carbon atom chains have been prepared by two routes which differ in the order in which the groups (methyl or alkenyl) were introduced. The ethers of p-tert-butylcalix[4]arene wer e isolated as a mixture of cone (minor) and partial cone (major) confo rmations in dynamic equilibrium. For the ethers of calix[4]arene the c onformational outcome depended on the method of synthesis. Up to three conformations could be detected: a cone, a partial cone with an anisy l unit inverted, and a partial cone with an alkenyl-bearing ring inver ted. H-1 NMR analysis of the complexes formed between these ethers and alkali metal iodides showed that both cone and partial cone complexes of the p-tert-butylcalix[4]arene tetraethers could be detected with l ithium iodide, but only cone complexes with the calix[4]arene derivati ves. Sodium iodide complexes were also formed with both sets of compou nds but in all cases only the cone complex was detected. (C) 1997 Else vier Science Ltd.